1. Field of the Invention
The field of art to which the claimed invention pertains is the catalytic cracking of hydrocarbons. More specifically, the claimed invention relates to a process for the utilization of hydrogen obtained by water thermolysis in a fluid catalytic cracking process.
2. Description of the Prior Art
There are a number of continuous cyclical processes employing fluidized solid techniques in which carbonaceous materials are deposited on the solids in the reaction zone and the solids are conveyed during the course of the cycle to another zone where carbon deposits are at least partially removed by combustion in an oxygen-containing medium. The solids from the latter zone are subsequently withdrawn and reintroduced in whole or in part to the reaction zone.
One of the more important processes of this nature is the fluid catalytic cracking (FCC) process for the conversion of relatively high-boiling hydrocarbons to lighter hydrocarbons boiling in the heating oil or gasoline (or lighter) range. The hydrocarbon feed is contacted in one or more reaction zones with the particulate cracking catalyst maintained in a fluidized state under conditions suitable for the conversion of hydrocarbons.
The selectivity to the desired gasoline fraction in the FCC process is limited by the overall hydrogen balance, i.e. the available hydrogen. Although the providing of hydrogen gas from an outside source in the range of a few weight percent of the feed or even a few weight ppm would greatly enhance the FCC process selectivity, hydrogen is expensive and is generally not considered for addition to that process. For example, in U.S. Pat. No. 3,413,212 the advantages of hydrogen addition to the FCC process are shown, but reliance is placed on expensive and impractical means such as hydrogen donor materials added to the charge stock from external sources or derived by partial hydrogenation of aromatic hydrocarbons in the charge stock.
In U.S. Pat. No. 3,963,830 it is disclosed that crystalline zeolite structures, into which certain trivalent cations are added by cation exchange procedures, are capable of thermochemically decomposing water (water thermolysis) in a cyclic process which alternates the production of oxygen and hydrogen. In one part of the cycle the trivalent cations are reduced while interracting with water and the water molecules are decomposed with the consequent evolution of oxygen. In the other part of the cycle the bivalent metal cations are reoxidized by imposing different operating conditions also in the presence of water.
I have discovered a technique for utilizing water thermolysis in the FCC process so as to make hydrogen available in the cracking reaction and to achieve improved cracking selectivity and reduced coke production.